In my U.S. Pat. No. 3,990,687 issued Nov. 9, 1976 and entitled SHOCK ABSORBER WITH CONTROLLED FLUID BYPASS MEANS there is disclosed a shock absorber in which the control of fluid bypassed from one side of a piston head to the other working within a cylindrical casing is achieved by caging the piston head and the fluid bypass control elements so that proper alignment will always be realized. The shock absorber disclosed is primarily for use on motorcycles and is more or less vertically oriented to absorb bumps and other similar shocks.
In the case of certain vehicles, particularly motorcycles, when the same are rapidly accelerated, the weight of the rider and the rapid acceleration combine to increase the load on the rear wheel. With this increased load, a rapid series of small shocks will result in the piston head and piston rod working further into the hydraulic cylinder against the bias of the external spring. In other words, the damping against return movement is too great to permit complete return of the piston within the time between successive rapid shocks. When the vehicle rapidly decelerates, the load as a consequence of the weight of the driver tending to be thrown forwardly is taken on the front wheel and is decreased on the rear wheel with the result that the piston head and piston rod work further out from the cylinder under the bias of the external spring. This latter action is often referred to in the art as "pumping down". If large bumps or sudden shocks during either acceleration of decelerating conditions occur, with the piston head of the shock absorber closer to one end or the other rather than in the desirable central position, it may seat with substantial impact against one or the other of the ends of the cylindrical casing.
It would be desirable to provide some type of fluid bypass flow control which would effectively decrease the resistance to damping fluid flow from one side of the piston head to the other under accelerating conditions and increase this resistance under decelerating conditions. Such an arrangement would then avoid the risks of impacting of the piston head with one end or the other end of the cylindrical casing under accelerating or decelerating conditions when a sudden bump or shock occurs.